This invention generally pertains to a technique for controlling the concentration of previously incorporated antimicrobial agents during processing of the fiber following the initial incorporation procedure. This technique may be used to increase, decrease or maintain essentially constant the antimicrobial agent concentration of a fiber. A need for such a technique will become apparent from the following discussion in which a particular problem in the art is advantageously solved by this invention.
Antimicrobial agents, such as 10, 10'-oxybisphenoxarsine (OBPA), are known to serve to provide protection against bacterial attack of thermoplastic fiber materials, such as nylon. The incorporation of OBPA also serves to reduce the occurrence of mildew and other undesirable growths on the fiber when in final form such as carpeting, etc. In the prior art, OBPA has been initially incorporated into molten nylon to ensure its inclusion in the spun fiber product. This procedure results in an essentially homogeneous distribution of the OBPA through the nylon fiber cross-section. U.S. Pat. No. 3,345,341 is illustrative of such prior technique. However, subsequent bath dyeing of the fiber results in a loss, often of up to 70%, of the previously incorporated antimicrobial agent from the fiber. The loss is believed to be due to leaching of the antimicrobial agent, resulting in an equilibrium proportioning of the agent between the solid phase of the fiber and the liquid phase of the dye bath. Obviously one would need to incorporate inordinately large amounts of the antimicrobial agent to ultimately obtain an antimicrobially effective final concentration in the carpeting when losses on the order of 70% are encountered.
In the past, this loss problem has been avoided by using solution dyeing procedures in which the dye is incorporated into the melt along with the antimicrobial agent during the melt-spinning stage. For example, certain nylon carpet containing melt incorporated OBPA is currently manufactured in this manner. However, solution dyed carpeting is only available in a rather limited number of shades and, of course, can only be dyed by the fiber manufacturer. It would be desirable for the fiber manufacturer to be able to sell undyed bulk fibers which contain the antimicrobial agent so that the buyer can then process such bulk fiber into carpeting and then either dye the carpeting or have such operation performed at a custom dye house. This procedure would provide greater latitude as to color selection and provide greater flexibility in the overall manufacturing process. It is believed that the process of this invention overcomes the above mentioned problems in a highly advantageous and efficient manner.